Question

Categorise the given summary equations under respective phases and select the correct option.
I. $C _{6} H _{12} O _{6}+2 NAD ^{+}+2 ADP +2 Pi \rightarrow$
$2 C _{3} H _{4} O _{3}+2 ATP +2 NADH +2 H ^{+}$
II. Pyruvic acid $+4 NAD ^{+}+ FAD ^{+}+2 H _{2} O + ADP + Pi \rightarrow$
$3 CO _{2}+4 NADH +4 H ^{+}+ ATP + FADH _{2}$
III.

	$I$	$II$	$III$
A	Glycolysis	Fermentation	Krebs' cycle
B	Krebs' cycle	Fermentation	Glycolysis
C	Krebs' cycle	Glycolysis	Fermentation
D	Glycolysis	Krebs' cycle	Fermentation

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (D)

I. Glycolysis, also known as EMP (Embden, Meyerhof, Parnas) pathway, is the breakdown of glucose to pyruvic acid in the absence of oxygen. It occurs in the cytosol of the cell and completes in $10$ steps. Net reaction of glycolysis is:
Glucose$+2 NAD ^{+}+2 ADP +2 H _{3} PO _{4} \xrightarrow{\text { Glycolysis }}$
$2 \text { Pyruvate }+2 NADH +2 ATP +2 H ^{+}$
II. A molecule of pyruvic acid that enters a mitochondrion is completely oxidised to form 3 carbon dioxide molecules in one pre-Krebs' cycle decarboxylation and two Krebs' cycle decarboxylations. Net reaction of Krebs' cycle is as:
Pyruvic acid $+4 NAD ^{+}+ FAD ^{+}+2 H _{2} O + ADP + Pi \rightarrow$
$3 CO _{2}+4 NADH +4 H ^{+}+ FADH _{2}+ ATP$
III. Given reaction represents alcoholic fermentation. In alcoholic fermentation, pyruvate is converted into ethanol in a two step pathway. Ethyl alcohol fermentation is quite common in fungi (e.g., Rhizopus, yeast) and bacteria. In yeast, pyruvate is decarboxylated to form acetaldehyde which is then reduced by NADH to form ethanol.